class MoodCalendarService
  def self.generate_calendar(user, start_date: nil, end_date: nil)
    data = user.moods.includes(:mode)
      .order(:recorded_at)
      .map { |mood| { mode: mood.mode, recorded_at: mood.recorded_at } }

    day_logs_by_date = user.day_logs.index_by(&:day)

    if data.empty?
      start_date = Date.current
    else
      start_date ||= data.first[:recorded_at].to_date
    end

    start_date = start_date.to_date
    end_date = end_date ? end_date.to_date : [ Date.current, start_date + 5.months ].max
=begin
    if end_date.nil?
      end_date = start_date + 5.months
    else
      end_date = end_date.to_date
    end
=end

    data_by_date = data.group_by { |d| d[:recorded_at].to_date }
      .transform_values { |entries| entries.max_by { |e| e[:recorded_at] } }

    last_mode = data.select { |d| d[:recorded_at].to_date < start_date }
      .max_by { |d| d[:recorded_at] }
      &.[](:mode)

    complete_data = (start_date..end_date).map do |date|
      day_log = day_logs_by_date[date]
      if data_by_date[date]
        last_mode = data_by_date[date][:mode]
        data_by_date[date].merge(day_log: day_log)
      else
        { mode: nil, recorded_at: date.to_datetime, guess: last_mode, day_log: day_log }
      end
    end

    complete_data.group_by { |d| d[:recorded_at].to_date.beginning_of_month }
      .map do |month_start, _|
        first_monday = month_start
        first_monday = first_monday.next_occurring(:monday) unless first_monday.monday?

        next_month_start = month_start.next_month.beginning_of_month
        next_first_monday = next_month_start
        next_first_monday = next_first_monday.next_occurring(:monday) unless next_first_monday.monday?

        month_end = next_first_monday - 1.day

        data_hash = complete_data.index_by { |d| d[:recorded_at].to_date }

        all_days = (first_monday..month_end).map do |date|
          data_hash[date] || { mode: nil, recorded_at: date.to_datetime, guess: nil, day_log: nil }
        end

        weeks = all_days.group_by { |d| d[:recorded_at].to_date.beginning_of_week(:monday) }
          .sort_by { |week_start, _| week_start }
          .map { |_, week_moods| week_moods }

        {
          month: month_start,
          weeks: weeks
        }
      end
  end
end